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Show Operational improvements with cofire include ability to fire at loads above 145,000 to 150,000 lb/hr which had previously been precluded by opacity emissions or fan limitations. Warmup with gas from a cold start gave low opacity episodes compared to coal startup. Problematic coals, including fines up to 45 percent, were fired without reducing load or increasing excess air to avoid opacity episodes. INTRODUCTION u.s. industry operates over 1,500 coal-fired stokers using a broad spectrum of coal feed and grate systems including spreaders, mass feed chain grates, and under feed stokers. Stoker boilers are typically over 30 years old and are increasingly difficult to maintain in a reliable, efficient condition and in compliance with environmental regulations. Many units have experienced derate and reduced availability and efficiency due to opacity problems, decreasing consistency in coal supplies, and fuel/air handling system limitations. Natural gas cofiring is receiving renewed attention as a resource to enable the stoker boilers to recover lost performance and continue reliable service. The term "cofire" in industrial coal-fired boilers has long been used for the installation of one or more sidewall burners over the stoker. These burners were installed on both new units and, more commonly, on a retrofit basis for warm-up, coallightoff, and standby for coal interruptions. In the majority of cases, the burners were not intended for sustained gas cofiring simultaneously with coal. Accordingly, there was typically no cofiring performance demands engineered into the retrofit beyond the requirement to deliver heat stably into the firebox. In the majority of cases, these burners were eoen register burners, typically of the DAZ series. The early" cofire" burners met the intended requirements of operational convenience and risk reduction but did not constitute a significant gas utilization market. Starting in 1990, the gas industry started evaluating whether the auxiliary gas burners could offer compelling benefits to boiler operators when used for sustained gas cofiring 2 |
